1. Field of the Invention
This invention relates to the deposition of films of ordered polycrystalline material.
2. Description of the Prior Art
As is well known, sputtering apparatus has a chamber adapted for the removal of material from a target by ionic bombardment and for the deposition of that material on the surface of a selected object.
It has long been desired to find ways to use sputtering apparatus to consistently produce high-quality films of ordered polycrystalline material. In such films, certain of the characteristics of the material are substantially the same as in a wafer of the material cut from a single crystal. This correspondence occurs because the responses of the individual crystallites to physical stimuli add coherently. For example, films of ordered polycrystalline zinc oxide have substantially the same piezoelectric properties as single-crystal zinc oxide. Therefore, such films are useful for fabricating devices which utilize the piezoelectric properties of the material such as, for example, surface acoustic wave devices.
Such films of ordered polyscrystalline zinc oxide having strong piezoelectric properties have been successfully formed in various sputtering equipments under controlled laboratory conditions. However, the procedures followed have not given consistent results. Some of the zinc oxide films deposited using prior-art techniques are of excellent quality but other films, deposited under what appear to be identical or similar conditions, are relatively amorphous and therefore of poor quality. Such inconsistency and lack of reproducibility has precluded use of these procedures in a production environment. The unavailability of means for consistently and repeatably forming ordered films of polycrystalline material has, for example, inhibited wider use of piezoelectric films and surface acoustic wave phenomena in a variety of integrated devices.